Installing and Setting Up the Mortiser Cutter

With our hollow-chisel and auger sharp, we’re almost ready to go. All that remains is to install and set-up the cutter.

First, I install the auger and hollow chisel into the mortiser’s chuck and chisel sleeve respectively. There is one absolute in this process: you do not want to simply insert the auger and hollow chisel into their stops and tighten them in place. This causes the auger and interior of the hollow chisel to contact each other and generate excessive heat. A gap between the two is necessary to avoid heat levels that will burnish the wood and expose the auger and hollow chisel to damaging heat. To prevent contact and create the gap the auger is lowered during the installation process.

A controversy comes into play when determining the size of the gap. Unsubstantiated reports claim an extra 50 to 60 degrees of heat can be generated by too small a gap. Others report that softwood requires a larger gap than hardwood. Still others say the larger the cutter, the larger the required gap. I don’t necessarily disagree with any of these claims, but I like to keep my installation process simple and quick. So here’s how I do it.

I insert the auger into the hollow chisel. The auger will extend out the top of the hollow chisel with enough extending out the top of the hollow chisel to be secured in the mortiser’s chuck. I then insert the auger bit fully into the mortiser chuck and insert my thumbnail between the top of the hollow chisel and the bottom of its mounting sleeve and then tighten the auger chuck. Next, I remove my thumb, push the hollow chisel all the way into its sleeve, and tighten it in place.

As I operate the mortiser I monitor my cut to ensure the cutter is not overheating. If excessive squealing, smoking, or burnishing develops, the gap may be too small. Also, bear in mind the larger the gap, the more manual cleanup the bottom of the subsequent mortise will require—this definitely is a balancing act.

With the cutter installed, focus on adjusting the chisel parallel to the fence.

Adjusting the fence parallel to the chisel is important to ensure your mortise wall is parallel to the side of your stock along the mortise. I use bar stock to both ensure the parallelism of the chisel and fence and to set the fence at the appropriate location for my joint. This technique decreases layout time, since I only have to mark a start and stop line on the stock for each mortise I’m cutting.

Next, I set the depth of the mortiser’s cut. Begin this process by marking the desired depth on the stock’s end. If I have “extra” stock depth, I’ll set the bottom of the hollow chisel to this mark. Then the auger, which extends past this point due to the gap, will make the mortise a little deeper than required, how much being dependent on the size of the gap, and will allow me to possibly skip cleaning up the bottom of the mortise later. However, if I don’t have extra depth material, I’ll set the bottom of the auger to my depth layout line and plan on cleaning up the bottom of the mortise later.

Some other things you should check…

I don’t mean to discount these next two steps, because they are important. However, I don’t do them with every operation set-up because they generally remain accurate once set-up. But I do perform them when I get a new mortiser and a new cutter. After that, I view them more as a troubleshooting aid.

First, check that your cutter is square to the table. I perform this check both on the front and side of the chisel. If it is out of square, consult your owner’s manual and make the appropriate adjustment.

Second, ensure your mortiser’s fence is square to the table. Again, your owner’s manual should have a procedure for correcting an out of square fence.